I am looking to buy some new icing nozzles (for piping) and wondered which ones people would say are their "must have" nozzles? Which size do they recommend etc? I especially want a nice big star but dont know whether to get an open or close star and is size 8 big enough?

Sorry, but do you mean "tips"? And 'which ones" - well, it all depends upon what you are piping. I have a slew of tips that I don't use often, but I have them in case. I like the round ones of various sizes, and same for the leaf tips, straight. They aren't expensive, start building a collection.

yes sorry I mean tips. It's mainly for cupcakes

No worries, I was wondering if there was another style of cake dec'g item I was going to have to research!

I picked up a copy of the "Ateco" guide to cake decorating - it's about $5 and it shows what most tips can do, it was good to see what all the varieties can do! It's small and it's a great little reference. Granted, I do mostly fondant work w/royal icing accents, but I'm going to get better at more buttercream only cakes.

Since tips are so cheap, I tend to have at least one of each. For the more popular ones, I have two each (in case I need two colors of icing, so I don't have to wash the tip between colors). I recommend getting several different tips, so you have choices.

I would recommend that you get something like the Ateco guide that Wendl mentioned above and maybe a starter kit of different tips (Wilton makes kits with different numbers of tips - 24 and 52, or something like that) so that you could experiment with different sizes and shapes. It can be fun, and just playing around will give you lots of new ideas for your cupcakes. Then you can decide ir there any that you need more than one of. Also be sure to get some icing couplers for you decorating cones. These allow you to change tips on the same cone so you can make more than one kind of piping with the same color. Have fun!